Urolithiasis and Chronic Kidney Disease in Cats

Investigators at the Université de Montréal, Quebec, Canada, have identified an association between urolithiasis and chronic kidney disease in cats. The report was published in the Journal of the American Veterinary Medical Association.

Urolithiasis—particularly nephrolithiasis—has been found to increase the risk for chronic kidney disease in humans, say the authors.

The goal of the current study was to determine whether a similar association was present in cats. The authors point out that their study was designed to show only association, not cause and effect, so their results do not prove that urolithiasis is a risk factor for kidney disease (or vice versa).

The researchers examined the records of 126 cats (59 with and 67 without urolithiasis) seen at the veterinary school at the Université de Montréal between June 1, 2006, and July 31, 2013. Cats included in the study had serum creatinine concentration and urine specific gravity measured within 14 days of an ultrasound of the abdomen or urinary tract. The control group was selected randomly from cats that met the inclusion criteria and did not have urolithiasis. Exclusion criteria were urinary tract obstruction, renal mineralization, and the presence of a urinary catheter.

Age, weight, breed, and male:female ratio did not differ significantly between the two groups. The mean age of the urolithiasis group was 8.3 years; that of the control group was 8.7 years. Both groups included more male than female cats (33 of 59 cats with urolithiasis and 39 of 67 cats without urolithiasis were male).

The investigators defined chronic kidney disease according to International Renal Interest Society (IRIS) guidelines, with staging based on serum creatinine concentration and urine specific gravity. Significantly more cats in the urolithiasis group (56%) than in the control group (30%) had chronic kidney disease. The researchers found no significant association between IRIS stage and the presence of urolithiasis.

Two-thirds of the cats with urolithiasis had nephroliths, and about half had cystoliths. Fewer than 10% had urethroliths or ureteroliths. The analysis revealed no significant associations between chronic kidney disease and the presence of stones in the kidneys, ureters, or urethra. However, chronic kidney disease was negatively associated with the presence of bladder calculi. The authors suggest that this negative association could be attributed to different factors causing stone formation in the kidneys and the bladder.

Slightly more than one-fourth of the cats with urolithiasis had stones in multiple locations. The prevalence of chronic kidney disease in these cats was not significantly different from that in cats with uroliths in only one location.

Of the cats with nephroliths, 49% had stones in the renal pelvis, 23% had stones in the diverticula, and 28% had calculi in both locations. The location of stones within the kidney was not associated with the prevalence of chronic kidney disease.

The authors note that the prevalence of chronic kidney disease in both groups was higher than indicated in other studies. Their study population probably did not reflect the general cat population, they write, adding that they could not evaluate potential biases such as hydration status and administration of fluid therapy because of the retrospective nature of the study.

Other study limitations listed by the authors are the sample size and the exclusion of cats with renal mineralization, which can be difficult to distinguish from nephroliths. A larger sample might have uncovered more differences between the groups, they write, and using radiography in addition to ultrasonography might have identified more cats with nephroliths.

The authors recommend prospective studies to assess the risk factors for urolith development and further explore its association with chronic kidney disease.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.